Circular Linked List

COMP104 Circular Linked List / Slide 2 Circular Linked Lists * A Circular Linked List is a special type of Linked List * It supports traversing from the end of the list to the beginning by making the last node point back to the head of the list * A Rear pointer is often used instead of a Head pointer Rear

COMP104 Circular Linked List / Slide 3 Motivation * Circular linked lists are usually sorted * Circular linked lists are useful for playing video and sound files in “looping” mode * They are also a stepping stone to implementing graphs, an important topic in comp171

#include using namespace std; struct Node{ int data; Node* next; }; typedef Node* NodePtr; Circular Linked List Definition

COMP104 Circular Linked List / Slide 5 Circular Linked List Operations * insertNode(NodePtr& Rear, int item) //add new node to ordered circular linked list * deleteNode(NodePtr& Rear, int item) //remove a node from circular linked list * print(NodePtr Rear) //print the Circular Linked List once

COMP104 Circular Linked List / Slide 6 void print(NodePtr Rear){ NodePtr Cur; if(Rear != NULL){ Cur = Rear->next; do{ cout data << " "; Cur = Cur->next; }while(Cur != Rear->next); cout << endl; } Traverse the list Rear

COMP104 Circular Linked List / Slide 7 Insert Node * Insert into an empty list Rear 10 New NotePtr New = new Node; New->data = 10; Rear = New; Rear->next = Rear;

COMP104 Circular Linked List / Slide 8 * Insert to head of a Circular Linked List Rear New New->next = Cur; // same as: New->next = Rear->next; Prev->next = New; // same as: Rear->next = New; PrevCur

COMP104 Circular Linked List / Slide 9  Insert to middle of a Circular Linked List between Pre and Cur Prev New New->next = Cur; Prev->next = New; RearCur

COMP104 Circular Linked List / Slide 10 * Insert to end of a Circular Linked List Rear New New->next = Cur;// same as: New->next = Rear->next; Prev->next = New;// same as: Rear->next = New; Rear = New; Prev Cur

void insertNode(NodePtr& Rear, int item){ NodePtr New, Cur, Prev; New = new Node; New->data = item; if(Rear == NULL){// insert into empty list Rear = New; Rear->next = Rear; return; } Prev = Rear; Cur = Rear->next; do{// find Prev and Cur if(item data) break; Prev = Cur; Cur = Cur->next; }while(Cur != Rear->next); New->next = Cur;// revise pointers Prev->next = New; if(item > Rear->data) //revise Rear pointer if adding to end Rear = New; }

COMP104 Circular Linked List / Slide 12 * Delete a node from a single-node Circular Linked List Rear = Cur = Prev Rear = NULL; delete Cur; 10

COMP104 Circular Linked List / Slide 13 Delete Node * Delete the head node from a Circular Linked List Rear Cur Prev->next = Cur->next; // same as: Rear->next = Cur->next delete Cur; Prev

COMP104 Circular Linked List / Slide 14  Delete a middle node Cur from a Circular Linked List Prev Rear Cur Prev->next = Cur->next; delete Cur;

COMP104 Circular Linked List / Slide 15 * Delete the end node from a Circular Linked List Rear Prev->next = Cur->next; // same as: Rear->next; delete Cur; Rear = Prev; Prev Cur

void deleteNode(NodePtr& Rear, int item){ NodePtr Cur, Prev; if(Rear == NULL){ cout << "Trying to delete empty list" << endl; return; } Prev = Rear; Cur = Rear->next; do{// find Prev and Cur if(item data) break; Prev = Cur; Cur = Cur->next; }while(Cur != Rear->next); if(Cur->data != item){// data does not exist cout << "Data Not Found" << endl; return; } if(Cur == Prev){// delete single-node list Rear = NULL; delete Cur; return; } if(Cur == Rear) // revise Rear pointer if deleting end Rear = Prev; Prev->next = Cur->next;// revise pointers delete Cur; }

void main(){ NodePtr Rear = NULL; insertNode(Rear, 3); insertNode(Rear, 1); insertNode(Rear, 7); insertNode(Rear, 5); insertNode(Rear, 8); print(Rear); deleteNode(Rear, 1); deleteNode(Rear, 3); deleteNode(Rear, 8); print(Rear); insertNode(Rear, 1); insertNode(Rear, 8); print(Rear); } Result is: